U.S. patent number 4,892,068 [Application Number 07/364,745] was granted by the patent office on 1990-01-09 for geared automatic compression release for an internal combustion engine.
This patent grant is currently assigned to Kohler Co.. Invention is credited to Jeffrey P. Coughlin.
United States Patent |
4,892,068 |
Coughlin |
January 9, 1990 |
Geared automatic compression release for an internal combustion
engine
Abstract
An internal combustion engine is provided with a mechanism to
release engine compression at low speeds thereby facilitating
starting of the engine. The engine has an exhaust valve which is
operated by a valve lifter following a cam surface. A cam pin is
positioned within a seat in that cam surface in a manner which
allows the pin to rotate. A drive member is attached to the cam pin
and has gear teeth in a peripheral edge. A flyweight has teeth
which engage the gear teeth of the drive member and cause a
rotation of the cam pin in response to engine speed. At relatively
low engine speeds an eccentric portion of the cam pin extends above
the cam surface so as to engage the valve lifter producing an
opening of the exhaust valve during the compression portion of the
engine cycle. At higher engine speeds the cam pin is rotated so
that the eccentric portion of the cam pin no longer extends above
the cam surface so that the exhaust valve is not opened during the
engine compression. This operation automatically release of the
compression at lower engine speeds.
Inventors: |
Coughlin; Jeffrey P. (Kaukauna,
WI) |
Assignee: |
Kohler Co. (Kohler,
WI)
|
Family
ID: |
23435888 |
Appl.
No.: |
07/364,745 |
Filed: |
June 9, 1989 |
Current U.S.
Class: |
123/182.1;
123/90.16 |
Current CPC
Class: |
F01L
13/085 (20130101); F02B 2275/22 (20130101) |
Current International
Class: |
F01L
13/08 (20060101); F01L 013/08 () |
Field of
Search: |
;123/90.16,90.17,182,316 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Lo; Weilun
Attorney, Agent or Firm: Quarles & Brady
Claims
I claim:
1. In an internal combustion engine having a valve, a valve lifter,
a cam shaft with a cam surface which engages the valve lifter to
open the valve at a first angular position of the cam shaft, and a
mechanism for opening the valve at a second angular position of the
cam shaft, the improvement in the mechanism comprising:
a cam pin located adjacent to the cam surface in a manner in which
said cam pin can rotate on its longitudinal axis, and having a
portion eccentric to the longitudinal axis which portion extends
above the cam surface to engage the valve lifter and open the valve
in a first rotational position and which portion in a second
rotational position does not engage the valve lifter in a manner
which opens the valve;
a drive member attached to said cam pin and having teeth in one
surface thereof; and;
a flyweight which rotates with the cam shaft and having teeth
meshed with the teeth of said drive member.
2. The improvement as recited in claim 1 wherein said flyweight is
crescent shaped and has the teeth along a concave edge surface.
3. The improvement as recited in claim 1 wherein said cam pin
rotates greater than 90 degrees between the first and second
rotational positions.
4. The improvement as recited in claim 1 wherein said cam pin is
received in a seat in the cam shaft.
5. In an internal combustion engine having a valve, a valve lifter,
a cam shaft with a cam surface which is engaged by the valve lifter
to open the valve at a first angular position of the cam shaft, a
gear mounted to the cam shaft, and a mechanism for opening the
valve at a second angular position of the cam shaft, the
improvement in the mechanism comprising:
a cam pin located adjacent the cam surface in a manner in which
said cam pin can rotate on its longitudinal axis, and having a
portion eccentric to the axis which portion extends above the cam
surface to engage the valve lifter and open the valve in a first
rotational position and which portion in a second rotational
position does not extend above the cam surface;
a drive member attached to said cam pin and having teeth in one
surface thereof; and
a flyweight pivotally mounted to the gear and extending in a plane
substantially orthogonal to a longitudinal axis of the cam shaft,
said flyweight having teeth which engage the teeth of said drive
member.
6. The improvement as recited in claim 5 wherein the eccentric
portion of said cam pin is designed so that the valve lifter
contacts the cam surface before disengaging contact with the cam
pin during each rotation of the cam shaft when the cam pin is in
the first rotational position.
7. The improvement as recited in claim 6 wherein said cam pin is
received in a seat in the cam shaft.
8. The improvement as recited in claim 5 wherein said flyweight is
crescent shaped having a first end pivotally attached to the gear
and a second end having the teeth along a concave edge of the
flyweight.
9. The improvement as recited in claim 5 wherein said drive member
comprises a plate having an aperture in which said cam pin is
fixedly received.
Description
BACKGROUND OF THE INVENTION
The present invention relates to compression release mechanisms for
internal combustion engines which operate a valve at low engine
speeds to release pressure within the engine cylinder during the
compression portion of the combustion cycle.
It is desirable in internal combustion engines to reduce the force
required to turn over the engine during starting. It is
particularly advantageous to reduce the starting forces in small
internal combustion engines which are to be started by hand. In
addition, such hand started engines must provide a mechanism to
eliminate the danger of physical injury from engine kickback.
The chief cause of difficulty in turning over an internal
combustion engine is the engine compression. The prior art is
replete with mechanisms for releasing or reducing compression
during starting. Early devices provided a manually operated valve
which released the pressure from the cylinder during starting. The
disadvantage of such a manual valve is that it must be quickly
closed by the operator after cranking in order for the engine to
start. The manual operated valve requires a certain amount of skill
in order to properly start the engine and is susceptible to
operator oversight. The prior art also teaches a variety of
automatic compression release mechanisms which are governed by the
speed of the engine. At low engine speeds the compression release
mechanism opens a valve during the compression portion of a
combustion cycle. When the speed increases above a given level, the
compression release mechanism no longer operates to open the valve
during the engine compression.
Many of the prior art devices utilized an existing engine cylinder
exhaust valve to release the compression during engine starting. In
this type of a device, the compression release mechanism operated
in conjunction with the cam shaft on which a valve lifter for the
exhaust valve rode. An example of this type of mechanism is shown
in U.S. Pat. No. 3,362,390. This device has a crescent shaped
flyweight which allows a latching pin to pivot less than 90.degree.
into different positions depending upon engine speed. In one
position, the latching pin engages a valve lifter raising the
lifter from a cam surface during engine compression. In prior
mechanisms of this type, the lifter dropped off the pin back onto
the cam surface at the end of the compression portion of the engine
cycle. This abrupt transition generated additional noise in the
engine. Furthermore, the latch pin was not rigidly held by the
flyweight in its normal operating position thereby allowing the pin
to move back and forth.
SUMMARY OF THE INVENTION
A compression release mechanism is incorporated into an internal
combustion engine having an exhaust valve and an associated valve
lifter. The valve lifter follows a cam surface on a cam shaft. A
cam pin is received within a seat in the cam surface so as to be
able to rotate within the seat along the pin's longitudinal axis.
The cam pin has a portion eccentric to its longitudinal axis, which
portion extends above the cam surface to engage the valve lifter in
a first rotational position, and which extends below the cam
surface in a second rotational position so as not to engage the
valve lifter. The cam pin is attached to a drive plate which has
gear teeth in a peripheral edge.
A drive mechanism is provided which engages the gear teeth of the
plate and causes it to rotate in response to engine speed. In the
preferred embodiment, the drive means comprises a flyweight
pivotally mounted on a timing gear fastened to the cam shaft
allowing the flyweight to rotate in a plane that is substantially
orthogonal to the cam shaft longitudinal axis. A portion of the
flyweight has gear teeth which mesh with the gear teeth of the
drive plate.
At low engine speeds, the drive mechanism engages the drive plate
to rotate the cam pin into the first rotational position thereby
forcing the valve lifter to open the valve during the compression
portion of the engine cycle. As the engine speed increases,
centrifugal forces acting on the drive mechanism rotate the drive
plate and the cam pin into the second rotational position. In this
second position the eccentric portion of the cam pin does not
engage the valve lifter to open the valve.
A general object of the present invention is to provide a mechanism
which automatically releases the compression of an internal
combustion engine at low speeds to facilitate starting the
engine.
A more specific object is to provide such a compression release
mechanism having an eccentric cam pin which is rigidly held in
different positions depending upon the speed of the engine. By
holding the pin in the different positions, it is not permitted to
move from those positions.
Another object of the present invention is to provide a flyweight
design which can be manufactured easily without complex metal
forming steps.
Yet another object is to provide a mechanism which can be assembled
easily.
A further object is that the compression release mechanism
incorporate components which can be easily fabricated and
assembled.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of a portion of an internal
combustion engine incorporating the present invention;
FIG. 2 is a view taken along line 2--2 of FIG. 1 and illustrates
the orientation of the components when the engine is stopped or at
low speeds; and
FIG. 3 is an illustration similar to that of FIG. 2, but which
illustrates the orientation of the components at a higher engine
speed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With initial reference to FIG. 1, an internal combustion engine 10
has a passage 12 which communicates with the engine cylinder (not
shown). The passage 12 opens into an exhaust outlet 16 and has a
valve 14 for selectively sealing the interface between the passage
and the exhaust outlet. The valve 14 is mounted on a first valve
lifter 18 which is biased by spring 20 to maintain the valve in a
closed state.
The cylinder passage 12 also communicates with a fuel intake port
22 which connects to a conventional carburetor (not shown). An
intake valve 24 selectively seals the interface between the
cylinder passage 12 and the fuel intake port 22. The intake valve
24 is attached to a second valve lifter 26 which is biased by
spring 28 to maintain the intake valve 24 in a closed position (as
illustrated in FIG. 1).
The remote ends of the two valve lifters engage a cam shaft 30
having a longitudinal axis 36. The cam shaft 30 includes a first
cam surface 31 which is followed by the first valve lifter 18. The
first cam surface 31 has a lobe 33 that pushes the first valve
lifter 14 upward to open the exhaust valve 14 when the cam shaft is
at a first angular position and release the combustion gases from
the engine cylinder. The cam shaft also includes a second cam
surface 32 which is followed by the second valve lifter 26 to open
the intake valve 24 so that a fuel mixture can enter the cylinder
from the carburetor. The operation of the exhaust and intake valves
have a conventional timing relationship to the movement of the
piston within the engine cylinder. This timing relationship is
maintained by a timing gear 34 attached to the cam shaft 30 and
meshing with a gear on the piston's crank shaft (not shown).
With reference to FIGS. 1 and 2, the engine 10 further comprises a
compression release mechanism, generally designated 40. This
compression release mechanism 40 includes a cam pin 42 having an
eccentric portion 44 at one end which is received within a seat 46
of the cam shaft 30. The eccentric portion 44 of the cam pin has a
semi-circular cross section, as best shown in FIG. 2. The end of
the cam pin 42 which is remote from the eccentric portion 44 is
located within an aperture 38 in the gear 34. The cam pin 42
loosely fits within the aperture 38 and the cam shaft seat 46 and
is able to rotate about the pin's longitudinal axis. A drive plate
48 is fixedly attached to the cam pin 42 and has gear teeth 49 in a
peripheral edge.
A generally crescent shaped flyweight 50 is attached to a major
surface of the timing gear 34 by a rivet 52 in a manner which
allows the flyweight to rotate about the rivet. For example, the
flyweight can be stamped from a sheet of metal without the need for
further bending. Although the flyweight is attached to a gear in
the preferred embodiment, any similar plate-like element fixed to
the cam shaft can be used. A torsion spring 54 extends around the
rivet 52 with one end 55 in contact with a surface of the cam shaft
30 and another end 56 bent around the outer edge of the flyweight
50 thereby biasing the flyweight 50 toward the cam shaft. The plane
of flyweight 50 is substantially parallel to the surface of the
gear and normal to the longitudinal axis of the cam shaft 30, as
shown in FIG. 1. A series of gear teeth 60 are cut in the inner
edge 61 of the flyweight 50 and mesh with the teeth 49 in the drive
plate 48. The use of meshed teeth to couple the flyweight and the
drive plate facilitates component assembly as compared to previous
automatic compression release mechanisms. As will be described in
detail, the movement of the flyweight 50 about the rivet 52 exerts
a force which produces a rotational movement of the cam pin 42.
FIG. 2 illustrates the orientation of the compression release
mechanism 40 when the engine is stopped or at relatively low speed.
In this orientation, the torsion spring 54 biases the flyweight 50
toward the cam shaft 30 which rotates the cam pin 42 into an
position where its eccentric portion 44 extends above the first cam
surface 31 represented by a phantom line. In this position the
drive plate 48 strikes the cam shaft 30, which limits the movement
of the compression release mechanism 40.
When cam shaft 30 rotates into the angular position illustrated in
FIGS. 1 and 2, this eccentric portion 44 engages the first valve
lifter 18 forcing it upward thereby opening the exhaust valve 14.
The location of the cam pin 42 about the cam shaft 30 is such that
this engagement occurs during the compression portion of the
combustion cycle. As a consequence, at low engine speeds, for
example below approximately 700-800 r.p.m., the eccentric portion
44 of the cam pin 42 will engage the first valve lifter 18 to open
the exhaust valve during the compression portion of each combustion
cycle. This engagement and opening of the exhaust valve 14 releases
the compression within the engine cylinder thereby reducing the
amount of force required to turn over the engine. As a result, less
force is required to turn over the engine at low engine speeds,
such as occur during engine starting.
As the speed of the engine increases, the centrifugal forces acting
on the flyweight 50 exceed the force of the torsion spring 54
causing the flyweight to pivot about rivet 52 away from the cam
shaft 30, as illustrated in FIG. 3. As the flyweight 50 pivots, its
gear teeth rotate the drive plate 48. The force exerted by the
flyweight on the drive plate 48 rotates the cam pin 42 counter
clockwise about its longitudinal axis. Above approximately 700-800
r.p.m., the centrifugal forces acting on the flyweight 50 maintain
it in the position illustrated in FIG. 3, where the drive plate 48
strikes the cam shaft 30 limiting the outward movement of the
flyweight. The speed at which the compression release ceases is set
to be slightly greater than the speed at which an electric starter
can turn over a warm engine, for example.
When the compression release mechanism is in the orientation
illustrated in FIG. 3, the eccentric portion 44 of the cam pin 42
is below the first cam surface 31 depicted by the phantom line.
Therefore, as the cam shaft 30 rotates through the compression
portion of the combustion cycle, the exhaust valve lifter 18
remains in contact with the first cam surface 31. When the exhaust
valve lifter 18 is in contact with this angular portion of the
first cam surface 31, it is not raised upward and the exhaust valve
14 remains closed during the compression portion. In this state of
operation, the compression within the engine's cylinder is not
being released so that at high engine speeds the engine piston is
compressing the fuel mixture whereby self-sustained engine
operation can occur.
By utilizing gear teeth to transfer the force from the flyweight 50
to the cam pin 42, the cam pin cannot move independently of the
flyweight. This provides a smooth controlled rotation of the cam
pin from one extreme position of its rotation to the other extreme
position (i.e. the positions illustrated in FIGS. 2 and 3).
Furthermore, the geared coupling of these elements rigidly holds
the cam pin in each of these extreme positions.
Although the present invention has been described in terms of
actuating the exhaust valve 14 to release the compression, the
intake valve 24 could have been used as a alternative. Even though
FIG. 1 illustrates a side valve engine where the valves are locate
in the crankcase to one side of the cylinder, the present invention
is equally applicable to overhead valve engines in which the valves
are located in a cylinder head.
* * * * *